I wonder if perhaps ancient polytheistic religions were less likely to have fundamentalist supporters, as they often lacked founding (fundamental) texts.
An observation of fundamentalists throughout history: Every one of them has felt certain that the end of the Universe is just around the corner
I don't know about Greek city states, but for much of its history the Roman Empire demonstrated considerable tolerance towards non-Roman religions. And judging by the success that Christianity and Islam had in gaining converts in their early years, it seems like polytheistic societies are often more open minded religion wise.